Aim: Graves's disease and thyroiditis can both characterized with thyrotoxicosis, but their clinical outcome and therapy is quiet different. Measurement of iodine uptake is the gold standard to differential diagnosis the thyroiditis or Graves's disease. But the iodine uptake is limited for its availability in china and easily influenced by medicine or food contained iodine.The blood pattern of thyroid CFDS is useful for differentiate the cause of thyrotoxicosis.Most previous studies using the descriptive pattern of thyroid CFDS is easily varied by operator subjective judgement. This study is focus on the role of peak systolic velocity of thyroid superior artery in differential diagnosis of thyrotoxicosis. Methods: Patients with thyrotoxicosis symptoms without recent medicine history were enrolled in two clinical center. Its thyroid function, iodine uptake , CFDS of thyroid and peak systolic velocity of thyroid superior artery is detected. Thyrotoxicosis is defined as TSH level below the low value of normal range. Graves disease is defined as the typical symptoms of graves disease such as graves ophthalmopathy or increased iodine uptake. Thyroiditis is defined as lack of typical symptoms of graves disease or decreased iodine uptake.We use receiver operator curve(ROC) to evaluate its diagnosis value